The present invention relates to an intermediate transfer member for temporarily holding an image in an image forming process according to electrophotography, and an electrophotographic apparatus including the intermediate transfer member.
An electrophotographic apparatus including an intermediate transfer member is very effective for forming a color image by sequentially superposing and transferring a plurality of component color images. For example, it is possible to decrease color deviation in superposing respective color toner images compared with a transfer process described in Japanese Laid-Open Patent Application (JP-A) 63-301960. Moreover, it is possible to transfer an image from the intermediate transfer member onto a recording medium or transfer-receiving material without necessitating holding means, such as glipper means, sucking means or curvature means (as disclosed in FIG. 1 of JP-A 63-301960), so that the recording medium can be selected from a wide variety of materials, including thin paper (40 g/m2) to thick paper (200 g/m2), wide to narrow medium, and long to short medium. Accordingly, transfer can be performed onto an envelope, a post card and even label paper, etc.
Because of such advantageous features, color copying machines and color printers using intermediate transfer members have already been available on the market.
The intermediate transfer member may assume a shape of a drum or a belt, and a belt-shaped intermediate transfer member is advantageous because it allows a reduction in entire apparatus cost and a broad latitude for disposition designing thereof.
However, a conventional intermediate transfer belt comprising resin or rubber has caused the following difficulties when supported under tension about a roller.
(1) The permanent elongation of the intermediate transfer belt is gradually increased until the belt slips on the roller so that a deviation (color deviation) is caused between respective color toner images when the toner images are transferred from the photosensitive member onto the intermediate transfer belt (primary transfer), thus failing to provide clear images.
(2) When the belt is biased on the roller to its side, the belt edge is abutted against the flange, etc., to be rubbed and damaged in some cases.
Against these problems, e.g., JP-A 3-293385 has proposed to reinforce a rubber-made intermediate transfer belt with backing polyamide woven cloth. In this case, however, as there is a large difference in electrical resistivity between the rubber and the woven cloth, the intermediate transfer belt is caused to have a very large thicknesswise resistivity depending on the material and the thickness of the woven cloth, thus failing to effect good electrostatic transfer. Further, the trace of the woven cloth can appear in the product image, preventing high-quality images.
On the other hand, JP-A 6-149079 discloses an intermediate transfer belt comprising PVDF or polycarbonate, but the belt lacks elasticity by itself, so that transfer failure such as hollow image dropout (i.e., middle image portion surrounded by a contour of image being not transferred) is liable to occur, and the belt is liable to be torn or cracked due to resin fatigue under repetitive use, thus involving problems regarding durability.
In addition to the above, U.S. Pat. No. 5,409,557, JP-A 62-293270, JP-A 3-293385 and JP-A 3-69166 have disclosed reinforcement of intermediate transfer belts with fiber, etc.
Accordingly, we have made various intermediate transfer belts of rubbery elastic material reinforced with fiber. As a result, we have discovered the occurrence of a new-type of difficulty (hereinafter called xe2x80x9ccore trace imagexe2x80x9d) that the fiber trace appears as a density irregularity in a product image in some cases.
An object of the present invention is to provide an intermediate transfer member which is free from permanent elongation even in repetitive use, excellent in durability and free from the occurrence of core trace image.
Another object of the present invention is to provide an electrophotographic apparatus including such an intermediate transfer member and capable of providing clear images free from color deviation or core trace image.
As a result of our study, it has been discovered that the above-mentioned core trace image has occurred in the case where the fibers constituting the core member embedded within the base layer of the intermediate transfer member are not disposed with a proper spacing between adjacent fibers.
According to the present invention accomplished based on the above finding and further study, there is provided an intermediate transfer member comprising a base layer, and a core member embedded within the base layer and comprising fibers disposed with a spacing of 50-300 xcexcm between adjacent fibers.
According to the present invention, there is further provided an electrophotographic apparatus, comprising:
an electrophotographic photosensitive member,
charging means for charging the electrophotographic photosensitive member,
imagewise exposure means for exposing imagewise the charged electrophotographic photosensitive member to form an electrostatic image,
developing means for developing the electrostatic image to form a toner image on the electrophotographic photosensitive member, and
an intermediate transfer member for temporarily receiving the toner image by transfer from the electrophotographic photosensitive member, wherein the intermediate transfer member comprising a base layer, and a core member embedded within the base layer and comprising fibers disposed with a spacing of 50-300 xcexcm between adjacent fibers.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.